Reverberation method and apparatus



Aug. 27, R -rs REVERBERATION METHOD AND APPARATUS Filed April 27, 1953 2Sheets-Sheet 1 HQ. l. ELC'SAi/RL QT /E ERASE OSCI LLATOR Aug. 27, 1957J. R BUTTS 2,804,499

REVERBERATION METHOD AND APPARATUS Filed April 27, 1953 2 Sheets-Sheet 2FIG .3.

A T EFGW 1 SOURCE 2 AMPLIFlER I'M A-/ AMPUHER -2 I 4A PH) (REH ERASEOSCJLLATOR United States Pater fiice 2,8fi4,49 Patented Aug. 27, 1957REVERBERATION METHOD AND APPARATU Joseph Raymond Butts, Cairo, Ill.

Application April 27, 1953, Serial No. 351,304

2 Claims. (Cl. 179-1) This invention relates to reverberation methodsand apparatus and more particularly to an electromechanical soundreverberating device.

Among the several objects of this invention may be noted the provisionof devices which artificially produce reverberations or echoes ofvarying intensity, interval and duration; the provision of suchreverberation devices which can be conveniently connected to anyelectrical signal source; and the provision of devices of the classdescribed which are simple and compact in construction and reliable inoperation. Other objects and features will be in part apparent and inpart pointed out hereinafter.

Briefly, the invention is directed to a reverberationproducing devicecomprising an electronic amplifier having at least two inputs and atleast two outputs, an electrical signal source connected to one input, atransducer connected to one output, an elongate magnetizable recordingmedium, an erase head for demagnetizing said medium, a recording headconnected to the other output and adapted to produce a magnetic patternin said medium in response to the electrical signal, a playback headconnected to the other input adapted to reproduce said electrical signalin response to said magnetic pattern, and means for moving said mediumpast said erase, recording and playback heads, respectively, whereby thereproduced electrical signal is delayed in time relative to said firstelectrical signal.

The invention accordingly comprises the constructions and methodshereinafter described, the scope of the invention being indicated in thefollowing claims.

in the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated,

Fig. 1 is a block diagram of a reverberation-producing device of thepresent invention;

Fig. 2 is a circuit diagram of the device, illustrating an exemplarysignal source; and,

Fig. 3 is a block diagram of an alternate embodiment of the presentinvention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

In the sound reproduction art it is frequently desirable to producereverberation eifects. However, conventional acoustical reverberationchambers are expensive and require substantial space While theartificial reverberation machines hitherto known are complex andexpensive. In accordance with the present invention, an electronicreverberation-producing device is provided which is compact, versatile,inexpensive and reliable.

Referring now to Fig. 1, an electrical signal source is indicated byreference letter S. Any of the conventional electrical signal sources,such as microphones, phonograph pickups, the audio sections of radio ortelevision receivers and the like, are equivalents for the purposes ofthis invention. This electrical signal source is connected to one inputof an electronic amplifier A (which includes the customary gain orvolume control for each input), one output of which is connected todrive a transducer unit T Which may be any suitable electroacoustictransducer, such as a loud-speaker, a line to a load or the like. Asecond output of amplifier A and an erase oscillator E are connected toa recording and erasing head REI-I. A playback head PH is interconnectedwith a second input of amplifier A. An elongate magnetizable recordingmedium M, shown in the form of a loop, is passed over the recording anderasing head REH and playback head PH in the direction indicated by thearrowhead. The recording medium is driven by a pair of pulleys P, one ofwhich is mechanically actuated by the customary drive motor and theother of which serves as an idler to maintain loop tension. The spacingbetween heads PH and REI-I may be varied by means of a reverse-threadedadjusting screw W.

Operation is as follows:

Any electrical representation of an audible frequency signal impressedby source S on the first input of amplifier A is amplified andtranslated into acoustic or sound energy by the transducer or aloud-speaker T. If the electrical output is also connected to therecording and erase head REH as indicated, a magnetized pattern replicaof the electrical signal is impressed upon the moving recording medium M(previously demagnetized by the action of erase oscillator E) by varyingthe magnetization thereof. This pattern (after a time interval) istransferred by the medium to playback head PH which retranslates themagnetic pattern into a reproduction of the electrical signal. Theprimary difference between the original signal and the reproduced signalis the delay in time of the latter, which is a function of the spacingbetween heads PH and REH and the speed of medium M. The reproducedsignal is similarly amplified by A and converted into sound energy byloud-speaker T, thus providing an echo or a reverberation. It will benoted that a portion of the reproduced or time-delayed signal is alsofed to head REH and itself reproduced to yield a second reverberation orecho. This occurs repeatedly. The number of reverberations obtainable iscontrolled by adjustment of the volume control associated With the inputto amplifier A from head PH. If the respective volume levels of theoriginal signal from S and the reproduced signal from PH are balanced orequal, then any one sound or signal will theoretically be reproduced orreverberated an infinite number of times, as each delayed signal iscontinuously recirculated through A (separated along the time axis fromits preceding signal only by a time increment). On the other hand, alesser or finite number of reverberations can be reproduced byattenuating the volume level of the input from the playback head PH toamplifier A, relative to the volume level from electrical signal sourceS. The loop arrangement for passing medium M first over an erasing-headsection and then a recording-head section and finally a playback head, 7

provides an endless or continuous supply to carry the signal between theheads for the time-delay increment.

Exemplary detailed circuits and specific components are shown in Fig. 2,source S consisting of a musical instrument, such as a guitar G, and amicrophone 1 in acoustical communication therewith. Wires 3 and 5 areconnected to the first input of amplifier A, comprising a volume control6-1, the rotor of which is connected to a control grid CG-l of aduo-triode vacuum tube V-l. A

mixer which provides a single mixed signal (made up of the amplified twoinput signals to (3-1 and G-Z) through a coupling condenser C-Z to gridCG-3 of a vacuum tube V-2. -2 and its associated components, resistorR-d, cathode resistor R-7, by-pass condenser (3-3 and primary P-l of aninterstage transformer X-l serve as a voltage amplifier to drive a poweramplifier stage comprising secondary S-l, duo-triode V-3 and primary P-Zof an output transformer X-2. Cathode K-3 and the center tap ofsecondary 8-1 are connected to ground. A secondary 8-2 of thistransformer is connected to loud speaker T by wires 7 and 9. Anappropriate D. C. potential source is connected at 13+ and B-. Thefilaments (not shown) for tubes V-ll, V-2 and V-3 are connected to theusual A. C. supply.

A second output from amplifier A is provided by connecting wires 11 and13 through an equalizing network, comprising a shunt-connected resistorR-8 and a condenser C-S, to a recording winding R of head REH. The A. C.output of a conventional circuit for an erase oscillator (shown in boxE) is connected through wires 15 and l? to an erase Winding Q and acoupling winding D of head REH. A portion of the A. C. erase oscillatoroutput signal is inductively coupled to winding B to provide A. C. biasduring recording. A playback winding L of head PH is connected throughwires 19 and 21 to the second input of amplifier A via volume control6-1.

The elongate magnetizable recording medium, which is a hard magneticmaterial possessing high coercivity (on the order of about 200-500oersteds) and preferably high retentivity, is passed over the softmagnetic pole pieces associated with windings Q, R and L, in that order.This medium, which may be wire, tape, coated tape, etc., is driven at asubstantially constant speed past the heads. If, as in one of thepreferable embodiments, a continuous loop is used, the joint should behomogeneous, or one of the known blanking circuits should be provided todeactivate the heads during the instant the joint passes thereover.Another useful 'form of recording medium is a coated or plated disc ordrum. Regardless of the particular species of recording medium, it isadvantageous to have an adjustable physical spacing between heads PH andREH and a variable-speed drive for the medium, so that the intervalbetween reverberations may be varied conveniently.

It will be noted that the construction of heads PH and REH are identicalin the illustrated embodiments so that their functions could beelectrically reversed by customary switch means, thus reversing, ineffect, the relative motion of medium M Without reversing the directionof rotation of the drive motor. The unused winding in head PH would thenbe used as an erase section. This would provide a long interval betweenreverberations represented by the time it would take medium M to travelfrom PH to REH via pulleys P. Any of the usual playback, recording anderase heads, made as separate units or combined, are operable for thepurposes of the present invention.

The alternate embodiment of Fig. 3 is basically similar in operation andconstruction to that described in regard to the embodiment of Figs. 1and 2. However, in the second embodiment, a second amplifier A-l, whichmay be identical or similar to amplifier A, is employed, and theamplifier input and output connections are modified in certain respects.For example, the electrical signal from source S is fed to the firstinputs of each of the amplifiers A and A-1, and the playback head PH isinterconnected to the second inputs of each of the amplifiers A andA-Jl. Also, the output of amplifier A is connected to transducer T, andthe recording and erasing head REH is connected to the output ofamplifier A-i, rather than to the output of amplifier A.

The operation of the Fig. 3 apparatus differs from that described abovein regard to Figs. 1 and 2 primarily in that the reproduced signal willrecirculate through a separate amplifier A-l. In another aspect, theelectrical sig- 4 nal energizing head REH is isolated from theelectrical signal driving transducer T. This arrangement providesadditional operating flexibility. If, in the first embodient, the levelof the reproduced or delayed signal to amplifier A exceeds the level ofthe original signal from source S, instability would result from thefact that each succeeding reverberation would be increasinglyaccentuated and override the original signal. By providing a separateamplifier to amplify the input signal from source S and recirculatingits time-delayed reverberations, the level of at least the firstreverberation can be made to exceed that of the original signal, and thelevel of succeeding reverberations can be attenuated from the latterlevel. Moreover, the rate of attenuation of succeeding reverberationsmay be controlled over a wider range.

Thus, the level of the original signal at the output of amplifier A isadjustable by the usual volume control associated with the originalsignal input (numeral 1-1) from source S. The volume control associatedwith the first input (numeral I-1A) of amplifier A-1 controls the energylevel of the electrical signals fed to head REH. The volume controlassociated with the second input (numeral I-2A) of the amplifier A-1controls the number of reverberations, i. e., the rate of attenuation ofsucceeding reproduced signals. The volume control associated with thesecond input (numeral 1-2) of amplifier A determines the over-all levelof the reproduced or reverberated signals. Either of the volume controlsassociated with inputs 1-2 or I-1A could be eliminated, if desired; anda fixed setting of either 1-1 or 1-2 could also be employed.

It will be understood that the many conventional audio amplifiercircuits in use today are suitable equivalents for the purposes setforth herein. It is preferred, however, that the amplifier be capable ofreproducing audible frequencies with substantially flat response. If theamplifier response curve is not fiat, the recirculating echoes may beattenuated in tone quality to some extent because of the deviation ofthe response curve. However, this is not usually noticeable to the earand in some instances, may provide a novel sonic effect.

Also, it will be noted that any of the known methods and apparatus usedin D. C. or A. C. erasing and biasing may be employed and that otherequalizing networks, for either postor pre-emphasis, or both, are usefulherein.

Further, it will be understood that for the purposes set forth herein anamplifier having, for example, only one output winding to which therecording head and a load (e. g., transducer T) are both connected, hastwo outputs. Similarly, an amplifier has two inputs if the signal fromsource S is mixed with the reproduced signal from PH externally of theamplifier, and the mixed signals are fed in through one channel to thefirst amplifier vacuum tube.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

I claim:

1. A reverberation-producing device comprising first and secondelectronic amplifiers each having at least two inputs and at least oneoutput, an electrical signal source connected to one input of each ofsaid amplifiers, a transducer connected to the output of the firstamplifier, an elongate magnetizable recording medium, an erase head fordemagnetizing said medium, a recording head connected to the output ofsaid second amplifier and adapted to produce a magnetic pattern in saidmedium in response to an electrical signal from said signal source,

a playback head connected to the other input of each of said amplifiersadapted to reproduce said electrical signal in response to said magneticpattern, and means for moving said medium past said erase, recording andplayback heads, respectively, whereby the reproduced electrical signalis delayed in time relative to the first said electrical signal.

2. A reverberation-producing device comprising first and secondelectronic amplifiers each having at least first and second inputs andat least one output, an electrical signal source connected to the firstinput of each of said amplifiers, an electroacoustical transducerconnected to an output of the first amplifier, an elongate magnetizablerecording medium, an erase head for demagnetizing said medium, arecording head connected to the output of said second amplifier andadapted to produce a magnetic pattern in said medium in response to theelectrical signal, a playback head connected to the second input of eachof said amplifiers adapted to reproduce said electrical signal inresponse to said magnetic pattern, means for moving said medium pastsaid erase, recording and playback heads, respectively, whereby thereproduced electrical signal is delayed in time relative to the firstelectrical signal, a first volume control for said first input of saidfirst amplifier adapted to vary the level of said electrical signal, asecond volume control for said second input of said first amplifieradapted to vary the level of said reproduced signal, and a third volumecontrol for said second input of said second amplifier adapted to varythe number of reverberations produced.

References Cited in the file of this patent UNITED STATES PATENTS1,947,621 Schreiber Feb. 20, 1934 2,105,318 Goldsmith Jan. 11, 19382,141,231 Trautwein Dec. 27, 1938 2,279,018 Wolfe Apr. 7, 1942

